(1) Field of the Invention
This invention relates to dry type rotary displacement compressors wherein no oils for lubrication, cooling and sealing are supplied to a compression space for producing oil-free compressed gases, and more particularly it is concerned with a screw compressor of the type described.
(2) Description of the Prior Art
In dry type (oil-free type) rotary displacement compressors, no oil is supplied to a compression space for housing rotors therein, but there is the risk of the oil for lubricating the bearings for journalling the rotors entering the compression space. The oil enters the compression space through clearances between the shafts connected to the rotors and the wall of the casing enclosing the shafts. Thus it has hitherto been usual practice to provide oil shield means between the shafts and the compression space. The oil shield means are known from Japanese patent application No. 134,532/78 (Japanese patent Laid-Open No. 55-64172), Japanese patent application No. 112,900/79 (Japanese patent Laid-Open No. 56-39361) and Japanese patent application No. 67,825/80 (Japanese patent Laid-Open No. 56-164281), for example.
The prior art referred to hereinabove is directed to concrete constructions of the oil shield means, and no proposals have been made to solve the problem with regard to the position in which the oil shield means is located and the construction of the oil shield means particularly suitable for the selected position that would provide a good combination of position and construction.